A tunable wide-angle narrowband perfect absorber based on an optical cavity containing hyperbolic metamaterials

We demonstrate that wide-angle narrowband absorption can be achieved from a microcavity where a hyperbolic metamaterial and a dielectric layer are sandwiched between two metal reflectors. As the incident angle changes, the phase-shift variation in the hyperbolic metamaterial can compensate that in the dielectric layer and, consequently, result in the angle-insensitive Fabry-Perot resonance in the proposed cavity. Silicon, indium tin oxide (ITO), and gold layers are used to construct the microcavity to produce a narrow absorption band in the near-infrared region. Our device exhibits good absorption stability over a wide angle range of incidence from 0° to 70°. Moreover, the absorption wavelength can be tuned by changing the thickness of the resonator. The presented absorber may find potential applications in the design of narrowband thermophotovoltaic emitters, sensitive detectors, filters, etc.